Such gyroscopes are conventionally used in inertial systems designed for navigation, as is the case, for example, for a gyroscopic compass which is adapted to provide a measurement of angle in relation to a reference direction which is that of geographical North (direction).
Axisymmetric gyroscopes of the Coriolis Vibratory Gyroscope (CVG) type, for example of the Hemispherical Resonance Gyroscope (HRG) or more generally said to be of type I, such as those described in the document ‘Type I and Type II micromachined vibratory gyroscopes' by Andrei M. Shkel, pages 586-593, IEEE/ION (Institute of Electrical and Electronic Engineers/Institute of Navigation’) PLANS 2006, San Diego, Calif., USA, operate open-loop and measure an absolute rotation angle based on a measurement of an angle representing the vibration position of the gyroscope relative to the measurement electrodes.
Such a gyroscope may also be used closed-loop through monitoring the vibration position via a control of the precession as is described in particular in the document FR 2 755 227.
In this case, the vibration position of the gyroscope is kept in a fixed position and the measurement is deduced from the control that it is necessary to apply to the gyroscope to keep it in this fixed vibration position. This type of operation is also called “gyroscopic feedback”. The values provided by the physical measurement then no longer correspond to an angle but to a rotation speed.
The measurements provided by these vibrating gyroscopes may be marred by errors that are essentially a function of the vibration position relative to the measurement electrodes. These errors are therefore variables depending on the vibration position.
These errors have the effect of reducing the level of precision of the values thus measured. It is therefore useful to seek to reduce these errors in order to improve the performance of this type of gyroscope.
In the context of closed-loop operation, or also of gyroscopic operation, the document EP 1 752 733 describes a method aiming to reduce such errors affecting the measured values so as to boost the performance of such measurement devices.
To do this, the symmetry in the errors of such gyrometers between two vibration positions of said gyrometers 90° apart is used as a starting point and, as a result, the mean value of these errors is reduced by changing the vibration position of the gyrometers between two vibration positions separated by 90°.
Throughout the duration of switching from one vibration position to another, this document foresees using a second closed-loop gyroscope, or another gyrometer, to provide a measurement of rotation speed in place of the first gyrometer when the latter is in the course of carrying out a change in vibration position and therefore cannot provide a pertinent measurement of the rotation speed to be measured.
However, it should be noted that in relation to the measurements provided by a gyroscope in open-loop operation the measurements provided by a gyrometer exhibit a reduction in the precision of the measurement provided which essentially linked with uncertainties introduced by the transformation that must then be applied to the control in order to obtain a rotation speed.